Cracking of heavy hydrocarbons with inert solids



C. E. ADAMS July 24, 1956 CRACKING OF HEAVY HYDROCARBONS WITH INERTSOLIDS Filed April 15 1951 QEAc-HQN 'PRODUCT Aun @H UENT EAQTOL Cio/usaFLunn Somos EJED HYDlocAlboN FEED Il' il...)

FLmmzAw-lom lO Q Cola Mm/M H EAT ExcHAMGaL Qb T057 Clbborrlez UnitedStates Patent CRACKING OF HEAVY HYDROCARBONS WITH INERT SOLIDS Clark E.Adams, Baton Rouge, La., assignor to Esso Research and EngineeringCompany, a corporation of Delaware Application April 13, 1951, SerialNo. 220,816

2 Claims. (Cl. 196S5) This invention relates to improvements in thethermal cracking of relatively heavy hydrocarbons such as crude residua.More particularly it relates to vapor phase cracking in the presence ofrather coarse particles of a dense, substantially non-porous andabrasion-resistant contact material, which particles are maintained inthe conversion zone as a dense fluidized bed. As coke is formed aroundthe fluidized Contact particles, it is continuously ground off and blownfrom the conversion zone to a separation zone for recovery and furtheruse.

In the treatment of heavy petroleum materials such as reduced crudewhich contains large quantities of low gravity tar and the like, it ispractically impossible to convert such feed stocks to valuable productsin the gasoline and gas oil range without simultaneously convertingsubstantial proportions of the charge to coke which usually interfereswith the continuance of the conversion process; also coke recovery hasnot been heretofore feasible to any great extent, thereby furtherdetracting from the economy of such processes. Particularly inconventional thermal units using cracking coils and drums, cokeformation has greatly restricted the permissible severity of theoperation and increased the frequency of shut-downs required forcleaning. Similarly, the rapid rate of coke formation resulting from thecracking of heavy hydrocarbons has precluded their treatment byiiXed-bed catalytic processes, and recovery of coke as such has beenentirely impractical in the latter. Moreover, the excessive cokeformation also rendered catalytic cracking of heavy hydrocarbons influid units impractical, inasmuch as the catalyst required regenerationat a very high rate and this in turn required the combustion ofsubstantially all the coke, which was produced in amounts far exceedingthe heat requirements of the conversionprocess. Such regeneration alsorequired the handling of tremendous amounts of solid catalyst and coke,it being remembered that even in present commercial fluid cracking unitsemploying gas oil as a feed, and requiring relatively moderate rates ofcatalyst regeneration, the catalyst alone'is being circulated at a rateof about 30 tons per minute. In view of the aforementioned diiiiculties,a practical process for converting heavy petroleum materials intovaluable distillate fractions and a recoverable coke product has longbeen looked for in the art and is the subject of the present invention.n z

The attached drawing illustrates a preferred arrangement of operatingthe novel process. Referring in detail to the. drawing, 1 represents areactor which is in the form of a cylindrical vessel. In the reactor abody of iiuidized solid particles 2 is maintained which particles arerather coarse, dense, inert, and attrition resistant. As an example, asuitable material of this sort is rounded sea sand, or one may use metalshot, ceramic beads orother particles of similar characteristics. Thesolid particles may range in size from 70 to 1000 microns, preferably150 to 500 microns, and have a packed density greaterthan 1, preferablybetween 1.2l and 4. Fluidization of the particles is maintained bykeeping the linear between the reaction Zone and the cyclone.

gas velocity in the reactor greater than 2 ft./sec., preferably between2 and 5 ft./sec. or at as high a velocity as possible without carryingan appreciable portion of the contacting solids from the bed.

A heavy hydrocarbon feed is introduced into the lowerpart of reactor 1through line 3 and distributor nozzle 4 at such a rate that under thereaction conditions there is sufficient time for the coking reaction totake place without a build-up of tarry residue which would cause loss ofuidization by agglomeration of the particles. Depending on reactionconditions, the hydrocarbon feed rate may be between about 0.1 to 4.0parts by weight per hour per weight of contact particles, allowing aresidence time for the hydrocarbon reactant of about 0.1 to 10 secondsor more. The process may be carried out at any temperature suitable forobtaining the desired product distribution, usually between 800 and 2000F., and preferably between 900 and l400 F. The pressure in the reactormay range between about 0 and 150 pounds, preferably between 5 and 25pounds per square inch gage.

The hydrocarbon feed may be a reduced crude obtained by atmospheric orvacuum distillation, representing, for instance, about 2 to 25 vol. percent of the Whole crude distilled. Typically such reduced crudes boilabove 900 to 1150 F. atmospheric equivalent) and have gravities betweenabout 0 and 20 API. However, instead of a reduced crude, other residualstocks such as clarified oil from catalytic cracking, pitch, tar fromvisbreaking and the like may similarly be used in the present process.Also the heavy hydrocarbon feed may be cut back with naphtha or otherlight products to reduce its viscosity. Alternatively, where the feed isVery viscous, it may be preheated before injection into the reactor tomake it more fluid, preheat temperatures ranging from about 200 to 1000F., or preferably from 600 to 800 F.

Furthermore the feed may be diluted with steam, recycle gas, or otherinert or hydrocarbon gases in amounts of about 500 to 5000 cubic feetper barrel, the diluent gas offering a convenient means for maintainingthe gas velocity in the dense uidized bed 2 at the desired level. Thediluent such as steam may be introduced into reactor 1 either throughline 3 as a mixture with the feed, or the diluent may be introducedseparately through one or more gas lines 5, or some diluent may beintroduced at either place.

Gaseous and normally liquid reaction products together with diluentleave the uidized solids reaction Zone overhead as a gas While the cokeformed around the sand particles and then ground off due to theincessant impingement of the articles upon each other is suspended inthe effluent gases. use of high velocity gas jets 6 in the sand bed, thejets being preferably attached to diluent lines 5. The eiuent gases arepassed through a separating device such as internal cyclone 7 where thefinely ground, solid coke is separated from the vaporized products anddiluent. Alternatively, the cyclone may be installed outside of thereactor, butin that case it is necessary to insulate it and to providefor make up of any heat lost in transfer of the products to the cyclone.Maintenance of the cyclone temperature substantially .at the levelprevailing in thev reaction zone is necessary as a portion of thevaporized product leaves the reaction zone very nearly at its dew pointand would be lost in the cycle by condensation on the separated coke, ifheat were lost from the products Moreover, condensation of such producttar on the coke would tend to cause agglomeration and reduce thedesiredl ease .of handling the coke product. The gaseousvand vaporizedproduct and ldiluent pass from cyclone 7 through line 8 is removed fromthe cyclone in a iiuidized condition Patented July 24, 1956l Cokeabrasion may also be accelerated by 3 through pipe 9 into which an"inert liuidizing gas is introduced at a suitahlerate `'through 'one 'ormore lines '10.' Thus the coke can be pneumatically transported infurther. pipes to retinery furnaces (not shown). or to otherconvenient'locatons.

As a furtherl alternative, the finely ground coke suspended in theproduct lvapors may be carried overhead from reactor 1 with the product`stream directly "through line 8 without any `mechanical separation Vandthe coke can "then be isolated in the product recovery system '(n'otshown) as a paste with a minor amount of tarry residue. This isolationcan be carried .out by means of settling and/or filtration such as in aDorr thickener, or 'by distilling off 'the volatile components leavingthe 'coke concentrated inthe residual fraction. This pasty mass of cokeand tarryresidue may be molded by means of heat and pressure intobriquettes for use as industrial or household fuel.

Heat of reaction lis preferably supplied to reactor 1 indirectly inanyone of numerous ways which are known per se and'which have noparticular bearing von the present invention, For example, asillustrated in `the drawing, the required heat may be supplied to theuidized solids in bed 2 by means of the heat exchanger 11 from anexternal furnace preferably using as fuel a portion of the coke orprocess gas produced in the unit. Of course, if desired, other availablefuels may similarly be used tosupply the heat required.

Alternatively, it ist also possible to supply the heat of reaction bydirect introduction of air or other oxygencontaining gas into the bottomof reactor 1 through line `5 or through similar lines specially providedfor this purpose and located below the feed inlet, whereby some of` thecoke formed on the sand by conversion of the hydrocarbon feed is burned.However, in such an arrangement it is desirable that the feed inlet 4 belocated at least one-tenth to one-third of the reactor height above theair inlet 6 so as to keep combustion of valuable feed components to aminimum. Still another alternative of supplying the heat of reactioninvolves the use of a more or less conventional two-vessel systemwherein cokeeoated solids from the reactor are transferred to aregenerator vessel where the burning reaction is carried out and the hotregenerated particlescontaining a large portion of the `resultingheatare then recycled to theireactor at a rate adequate to supply thenecessary heat of reaction. This last method, however, risthe leastdesirable one since it involves the loss-of the main advantages of thevpresent invention, which are, firstly, a one-vessel system requiringminimum .recirculation of 'contact particles, and secondly, a highdegree of coke recovery for use outside of the system in uncontaminated,readily usable form.

An example further illustrating the mode of operation as well as theadvantages of the present invention is given below.

Example A `reactor 1 substantially as shownin 4the drawing and having aninside diameter of 2.9 inches was charged with 3300 grams of 35-80 meshof rounded sea sandand the sand was uidized to form a dense, fixedbedzhaving a distinct upper level by introducing steam into the-bottomof the reactor. The reactor was maintained at 12-70 F. by means ofexternal heat and 2.4% South Louisiana vacuum residuum having a .gravityof 11.9 API `was fed through a spray nozzle 4 for a period ofthreeihours at a rate of 1480 grams per hour together with (550gramsfper hour of steam. Additional steam twas fedto the bottom of thereactor through diluent lines 5, below nozzle 4, at 1450 grams per hour.Product vapors and diluent were taken overhead through a sintered metalfilter, having an average porosityfof about 3'5 microns. The metaliilter was used instead offthe "cyclone-'separator shown in'thedrawing.The upward velocity of the-gas leaving'thedense, tluid'bed was Vabout2;'6"feettper=second,

of which about l.9 feet per second was attributable to the total 'steamdiluent introduced Vinto the vessel while the product gas and otherreaction vapors accounted for the other 0.7 foot per second of thevelocity of the gas phase leaving the reactor bed.

The withdrawn reaction products and diluent were recovered inconventional equipment for subsequent work up, and .after completion `of`the run the solids which previously constituted the fluid bed weredischarged from the reactor after cooling to room temperature. Thedischarged solids weighed 3:55() grams and showed on analysis `l0.9weig'ht ypercent carbon and 0.2 weightpercent hydrogen. Another solidfraction amounting to 682 grams was recoveredas a deposit from the'overhead metal iilter and showed .an analysis of 76.1 weight percentcarbon and 1.1 Aweight percent hydrogen. This lter deposit, althoughcontaminated with some sand due to the short disengaging space betweenthe solids bed and filter inthe'small-scale 'test unit employed, thusaccounts for 4nearly '60% of the total coke made in this relativelyshort run and illustrates the practicability of recovering a `majorlproportionof the total coke product in a'nearly pure statefromseparation means located at the top of a reactor operated in'accordancewith the present invention. In lother similar runs iilter deposits ofeven higher coke content havebeen recovered, running `up to 89.6 weightpercent carbon and 1.7 weight percent hydrogen, the remainder being ash.

Torecapitulate, this invention relates to improvements in the conversionof `relatively heavy hydrocarbons to form liquid products of lowerviscosity and coke in a relatively-pure, recoverable state, andparticularly includes processes wherein a heavy viscous 4hydrocarbon isheat treated atsufiiciently high temperatures -to form solid coke.instead'of tarry residues, in addition to the principally desired lightdistillate fractions. The treatment according to the present inventionis carried out in the presence of a solid material such as seasand onvwhich f the colte-forming constituents of the feed are deposited. Thecontact materially characteristically has a high density and coarseparticle size to permit high -gas velocity in the reactor withoutappreciable entrainment. Another important characteristic of the contactmaterial used is its high `resistance to attrition, which resistance isnecessary for the maintenance of rmore or less the original particlesize'distribution throughout an entire run which may last for yperiodsranging from a few days to several months. Furthermore, high attritionresistance is also required to avoid contamination of the coke productwith entrained iinestofabraded contactfmaterial.

In the preferred modification of Vthe invention nooxidativeregeneration' of the-contact rnaterial'is necessary, inasmuchas, -after the attainment of equilibrium conditions,the coke is abradedfrom the tiuidized contact material at a rate` which equals vits rate offormation on the contactl particles. 'Unlike the coarse, dense contactparticleswhichcontinuously settle back into the fluidizedbed inl theconversion zone, the abraded coke particles are entrained overhead fromthe reactor in the vaporized conversion products and are mechanicallyseparated from the latter at atemperature above the dew point of theoverhead products. The separated coke particles `are readily fluidizableand as such are easilytransportable. A proper Tamount of the recoveredcoke particles maybe burned in a furnace which is arranged in indirectheat exchange relation with rthe cracking zone so as to supply theheatof` reaction to the latter.

Having described the ypresent invention, including a preferredembodiment thereof, it will be understoodthat numerous I'modificationsand variations of the invention may "bemadebypersonsfskilled in theartwithout departingfrom `its scopefand spiritas defined Ain the appendedclaims.

1. A process vfor 'cracking reduced vcrude which comprises providing apermanent dense, uidized bed of -attrition resistant sand particleshaving a particle diameter of at least 150 microns and a packed densi-tybetween 1.2 and 4 in the lower portion and a dilute phase zone in theupper portion of a reaction zone kept at a tem perature between 900 and1400 F., injecting reduced crude into the dense bed of particles at arate of between 0.1 to 4.0 parts 'by weight per hour per part of sandparticles, also injecting a high velocity stream of a diluent gas nearthe bottom of the reaction Zone so as -to give a total gas Velocity inthe dense bed of about 2 to 5 feet/sec. but not in excess of theentrainment velocity of the sand particles, thereby causing an abrasionof coke deposited on the sand particles substan-tially at the rate ofits formation from the crude, withdrawing a stream of gaseous productscontaining the abraded coke suspended therein from the upper portion ofthe reaction zone wherein entrained san-d particles becomesubs-tantially disengaged from the gaseous stream, passing the gaseousstream into a separa-tion zone maintained within the upper portion ofthe reaction zone substantially at the same temperature as the reactionzone temperature, withdrawing a stream of gaseous products and a streamof finely powdered coke from `the separation zone, passing a portion ofthe recovered coke to an external combustion zone, supplying anoxygen-containing gas yto the combustion zone and supplying theresulting heat -to the reaction zone by indirect heat exchange wi-th thedense uidized bed so as to maintain the bed at the desired temperaturewithout returning the remaining coke to the reaction zone.

2. A process for cracking a heavy hydrocarbon oil feed which comprisesproviding a permanent dense, fluidized bed of attrition resistant inert,solid, inorganic particles selected from the group consisting of sand,metal shot and ceramic beads having a particle diameter of at least 150microns and a packed density between 1.2 and 4 in the lower portion anda dilute phase zone in the upper portion of a reaction zone kept at atemperature between 900 and 1400 F., injecting the heavy oil into thedense bed of particles at a rat-e of between 0.1 to 4.0 parts by weightper hour per part of inert particles, also injecting a high velocitystream of a diluent gas near the bottom of the reaction zone so as togive a total gas Velocity in the dense `bed of about 2 to 5 feet/sec.but not in excess of the entrain-ment velocity of lthe inert particles,thereby causing an abrasion of coke deposited on .the inert particlessubstantially at the rate of its formation from lthe feed, withdrawing astream of gaseous produots containing the abraded coke suspended thereinfrom the upper por-tion of the reaction Zone wherein entrained inertparticles become substantially disengaged from the gaseous stream,passing the gaseous stream into a separation zone maintained within theupper portion of the reaction zone substantially at the same temperatureas the reaction zone temperature, and separately withdrawing a stream ofgaseous products and a stream of iinely powdered coke from theseparation zone without returning the coke to the reaction zone.

References Cited in the le of this patent UNITED STATES PATENTS2,340,974 Myers Feb. 8, 1944 2,364,145 Hup-pke et al. Dec. 5, 19442,388,055 Hemminger Oct. 30, 1945 2,412,152 Huit Dec. 3, 1946 2,412,879Fischer Dec. 17, 1946 2,421,651 Reeves lune 3, 1947 2,428,715 MarisicOot. 7, 1947 2,436,160 Blanding Feb. 17, 1948 2,459,824 Leer Ian. 25,1949 2,464,257 Pelzer et al Mar. l5, 1949 2,471,104 Gohr May 24, 19492,542,887 Watson Feb. 20, 1951 2,585,984 Alexander et a'l. Feb. 19, 19522,606,144 Leler Aug. 5, 1952

1. A PROCESS FOR CRACKING REDUCED CRUDE WHICH COMPRISES PROVIDING APERMANENT DENSE, FLUIDIZED BED OF ATTRITION RESISTANT SAND PARTICLESHAVING A PARTICLE DIAMETER OF AT LEAST 150 MICRONS AND A PACKED DENSITYBETWEEN 1.2 AND 4 IN THE LOWER PORTION AND A DILUTE PHASE ZONE IN THEUPPER PORTION OF A REACTION ZONE KEPT AT A TEMPERATURE BETWEEN 900 AND1400* F., INJECTING REDUCED CRUDE INTO THE DENSE BED OF PARTICLES AT ARATE OF BETWEEN 0.1 TO 4.0 PARTS BY WEIGHT PER HOUR PER PART OF SANDPARTICLES, ALSO INJECTING A HIGH VELOCITY STREAM OF A DILUENT GAS NEARTHE BOTTOM OF THE REACTION ZONE SO AS TO GIVE A TOTAL GAS VELOCITY INTHE DENSE BED OF ABOUT 2 TO 5 FEET/SEC. BUT NOT IN EXCESS OF THEENTAINMENT VELOCITY OF THE SAND PARTICLES, THEREBY CAUSING AN ABRASIONOF COKE DEPOSITED ON THE SAND PARTICLES SUBSTANTIALLY AT THE RATE OF ITSFORMATION FROM THE CRUDE, WITHDRAWING A STREAM OF GASEOUS PRODUCTSCONTAINING THE ABRADED COKE SUSPENDED THEREIN FROM THE UPPER PORTION OFTHE REACTION ZONE WHEREIN ENTRAINED SAND PARTICLES BECOME SUBSTANTIALLYDISENGAGED FROM THE GASEOUS STREAM, PASSING THE GASEOUS STREAM INTO ASEPARATION ZONE MAINTAINED WITHIN THE UPPER PORTION OF THE REACTION ZONESUBSTANTIALLY AT THE SAME TEMPERATURE AS THE REACTION ZONE TEMPERATURE,WITHDRAWING A STREAM OF GASEOUS PRODUCTS AND A STREAM OF FINELY POWDEREDCOKE FROM THE SEPARATION ZONE, PASSING A PORTION OF THE RECOVERED COKETO AN EXTERNAL COMBUSTION ZONE, SUPPLYING AN OXYGEN-CONTAINING GAS TOTHE COMBUSTION ZONE AND SUPPLYING THE RESULTING HEAT TO THE REACTIONZONE BY INDIRECT HEAT EXCHANGE WITH THE DENSE FLUIDIZED BED SO AS TOMAINTAIN THE BED AT THE DESIRED TEMPERATURE WITHOUT RETURNING THEREMAINING COKE TO THE REACTION ZONE.